Doing the layout for the front suspension for my speedster build. Have a tube axle from Speedway and will be using 1/4 elliptical springs salvaged from the Model A front spring. Will also be adding some DIY friction shocks. Plan is to have 6 degrees caster. Question: Do the mounting points for the spring and shock on the axle have to be on the 6 degree axis? Rough layout showing upper and lower mounting points. On the layout, the mtg points are on a 4 degree angle, and only the upper friction shock mount coincides with the 6 degree castor/kingpin angle.
Are the shocks the upper locating arm? Technically they don’t need to be at the same caster angle, but it just makes everything easier and prettier to have everything in the same plane. If your shock arms are the locating arms, you should probably research lengths and what might happen if the uppers and lowers aren’t the same.
Yeah, upper friction shocks will act like the upper locating radius arms in a 4-link suspension (I’m ***uming). Just quickly checking my layout, and with a 3” upwards travel, caster would increase by 2 degrees. Somewhat familiar with the rear 5-link suspension in my 80 series Land Cruiser, and IIRC, upper arms arms are much shorter than the lower arms like GM A-bodies, but I’m a complete newb when it comes to suspension design.
You can have both upper and lower pivot points at vertical [or laying back] Then rotate the axle in the bracket to get the desired caster. With 1/4 elliptic suspension the lower springs will try and shorten with brake torque So if you can mount the axle closer to the upper pivot [or dead on] and further away from the spring ,it will lessen this spring wind up. I'm curious about the upper pivot you have in the drawing? it should be at the center of the shock, not where you've mounted it [green arrow]
Shorter upper links create default "anti dive" As the suspension compresses it induces more positive caster which fights the forces caused by brake torque on the axle centerline
Ok. I think I understand what you’re saying. Never thought about forces under braking. Will have to think about that some more. Regarding the pivot point for the friction shock, the rear wards portion would be fixed to the vertical tower, so the radius would be from your green arrow on the left. Much like the setup I posted before. That is my go to reference pic at the moment.
Full-scale layout. Not quite the same as the smaller scale layout. I really have to find that front spring to see how it flexes. Was watching a YT vid, and the guy beveled the ends of each leaf. Said it would soften the ride, at only about 11” long sticking past the end of the frame, I need to do everything to soften the spring rate (I just ***uming that). I would probably create a radius type end for looks.
Zig, your example car has the spring and another link below it as the locators. The shock has three pivot points, so it’s just wiggling around in there. Doesn’t really look like a very reliable or accurate setup to me.
Just checked the geometry. 3” upwards travel = 10 degrees of caster 3” downwards travel = 6 degrees of caster This is just me basing the layout on mostly aesthetics, but the bracket on the axle looks way too bulky as is. I just don’t know the size of the eye in the spring, so guessing it’s 1”.
Damn! Didn’t notice that either! I must be blind. I saw the rod and ***umed it was braking, but missed that link beside it. WTH!?
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